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Projections of Retina (4).docx

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McMaster University
Gautam Ullal

October 22 , 2012 Psych 2E03: Sensory Processes Projections of Retina (4) Retina, Hypothalamus, Pineal gland & Circadian rhythm - the link for photo-entrainment resides in retina - photo-entrainment: alignment or synchronizing of biological rhythms (cycles) to ambient light-dark cycles - connection between photo signals from outside and biological cycle - rods and cones – not the exclusive receptors of retina Vertebrates – “inverted” retina - light reaches the cones uninterrupted - in the ganglion cells there are photopigments - rods and cones – not the exclusive receptors of retina: we can have vision without rods and cones, not very clear or detailed vision, basic vision - investigating in animals, knock out cones rhodopsin, still basic vision meaning there are some other receptors found in the ganglion cells - specialized ganglion cells, not all ganglion cells - melanopsin ganglion cell: using biochemical stains - axons of melanopsin ganglion cell along optic nerve - axons of melanopsin ganglion cell traced to suprachiasmatic nucleus of hypothalamus - photopigments in ganglion cells orchestrating suprachiasmatic nucleus Melanopsin associated photoreceptive system - special ganglion cells - no direct connect to the optic chiasm The Neuroanatomical link: Melanopsin associated photoreceptive system - melanopsin associated with pineal gland Melanopsin-Melatonin & Carcadian Rhythm - melanopsin a photopigment - melatonin of pineal gland: sleep - nocturnal animals – once you start exposing to light the levels come down, in the night they go up - diurnal animals – difference in melatonin levels: in night we build up melatonin, sleep cycles go along with melanopsin - why are the systems different: different signal patterns in both systems Melanopson-Melatonin, in Nocturnal and Diurnal animals - melatonin: sleep - nocturnal animals: melatonin increases during day – day time sleepiness - diurnal animals: melatonin increases during night – light-time sleepiness - nocturnal animals: light>decrease melanopsin>increase melatonin>sleep - dirnal animals: light>decrease melanopsin>decrease in melatonin>wakefulness Mel
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